/*
 * Copyright (c) 2003, KNOPFLERFISH project
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following
 * conditions are met:
 *
 * - Redistributions of source code must retain the above copyright
 *   notice, this list of conditions and the following disclaimer.
 *
 * - Redistributions in binary form must reproduce the above
 *   copyright notice, this list of conditions and the following
 *   disclaimer in the documentation and/or other materials
 *   provided with the distribution.
 *
 * - Neither the name of the KNOPFLERFISH project nor the names of its
 *   contributors may be used to endorse or promote products derived
 *   from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
 * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
 * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
 * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
 * OF THE POSSIBILITY OF SUCH DAMAGE.
 */

package org.knopflerfish.bundle.http;

import java.util.ArrayList;
import java.util.Hashtable;
import java.util.List;
import java.util.Stack;

import javax.servlet.http.HttpSession;

public class HttpSessionManager
  implements Runnable
{
  // private constants

  private final static int CHECK_INTERVAL = 60;

  // private fields

  private final HttpConfig httpConfig;

  private final Thread sessionTimeoutThread;

  private static int count = 0;

  private boolean stopped = false;

  private final Hashtable<String, HttpSessionImpl> sessions =
    new Hashtable<String, HttpSessionImpl>();

  private final Stack<HttpSessionImpl> recycledSessions =
    new Stack<HttpSessionImpl>();

  // constructors

  public HttpSessionManager(final HttpConfig httpConfig)
  {
    this.httpConfig = httpConfig;

    sessionTimeoutThread = new Thread(this, "HttpServer-SessionTimeout");
    sessionTimeoutThread.setDaemon(true);
    sessionTimeoutThread.start();
  }

  // private methods

  private void removeSession(HttpSession session)
  {
    synchronized (sessions) {
      sessions.remove(session.getId());
    }
    try {
      session.invalidate();
    } catch (final IllegalStateException ignore) {
    }
  }

  private void reuseSession(HttpSessionImpl session)
  {
    session.destroy();
    synchronized (recycledSessions) {
      recycledSessions.push(session);
    }
  }

  // public methods

  public HttpSession createHttpSession()
  {
    HttpSessionImpl session;
    if (recycledSessions.empty()) {
      session = new HttpSessionImpl();
    } else {
      synchronized (recycledSessions) {
        session = recycledSessions.pop();
      }
    }

    session.init(count++);
    session.setMaxInactiveInterval(httpConfig.getDefaultSessionTimeout());
    synchronized (sessions) {
      sessions.put(session.getId(), session);
    }

    return session;
  }

  public HttpSession getHttpSession(String sessionId)
  {
    if (sessionId == null) {
      return null;
    }

    HttpSessionImpl session;
    synchronized (sessions) {
      session = sessions.get(sessionId);
    }
    if (session != null) {
      synchronized (session) {
        if (session.isExpired()) {
          removeSession(session);
          reuseSession(session);
          session = null;
        } else {
          session.join();
        }
      }
    }

    return session;
  }

  public void destroy()
  {
    if (sessionTimeoutThread != null) {
      stopped = true;
      sessionTimeoutThread.interrupt();
      try {
        sessionTimeoutThread.join();
      } catch (final InterruptedException ignore) {
      }
    }
  }

  // implements Runnable

  public void run()
  {
    final long sleepTime = CHECK_INTERVAL * 1000;

    while (!stopped) {
      List<HttpSessionImpl> sessionList = null;
      // Must create a copy to avoid concurrent modification of the sessions map.
      synchronized (sessions) {
        sessionList = new ArrayList<HttpSessionImpl>(sessions.values());
      }

      for (final HttpSessionImpl session : sessionList) {
        synchronized (session) {
          if (session.isExpired()) {
            removeSession(session);
            reuseSession(session);
          }
        }
      }

      try {
        Thread.sleep(sleepTime);
      } catch (final InterruptedException ignore) {
      }
    }
  }

} // HttpSessionManager
